1. Field of the Invention
The present invention generally relates to an optical printing apparatus for exposing light onto a photosensitive recording medium to form a gradation image. More specifically, the present invention is directed to such an optical printing apparatus. That is, while one column, or plurality of columns constituted by a large number of light emitting elements (e.g., LEDs and ELs), or switching elements (e.g., liquid crystal shutter elements) are arranged as a print head, the respective elements are independently controlled in response to image data so as to print out a gradation image in the optical printing apparatus.
2. Description of the Related Art
Various sorts of optical printing apparatuses have been developed as apparatuses employing instant films and simultaneous color paper, and are commercially available in the markets. In these optical printing apparatuses, light is exposed onto photosensitive recording media so as to form gradation images.
A conventional optical printing apparatus will now be explained with reference to a drawing. FIG. 36 is a perspective view for schematically indicating a structure of a print head used in one conventional optical printing apparatus as disclosed in, for instance, Japanese Patent Application Laid-open No. 7-256928.
In FIG. 36, white light emitted from a halogen point light source 100 is separated into red-colored light, green-colored light, and blue-colored light by way of a color liquid crystal (LCD) shutter 101. The R, G, B-colored light is continuously irradiated onto an edge surface of an acrylic rod 102 in a time shift manner. In this print head, the acrylic rod 102 is covered with a reflection foil on which aluminum and the like are vapor-deposited except for a light emitting plane thereof. Thus, this acrylic rod 102 owns such a function capable of effectively converting light entered from a rod edge surface into line-shaped light. As a result, the red line-shaped light, the green line-shaped light, and the blue line-shaped light are continuously irradiated onto a black/white shutter array 103 in a time shift manner.
In this case, 3 columns of pixel arrays corresponding to the red light, the green light, and the blue light are provided inside the black/white shutter array 103. These pixel arrays are driven in such a manner that only designated color light can pass therethrough. For example, when the red line-shaped light is irradiated, this red line-shaped light can pass through only one pixel array corresponding to the color light, whereas the other two pixel arrays are kept under shield condition. Then, the red line-shaped light, the green-shaped light, and the blue line-shaped light, which are modulated by the black/white shutter 103 are focused on a photosensitive paper 105 such as the spectra instant film manufactured by Polaroid Inc., by using a SELFOC lens array 104 (namely, tradename of converging lens array). At this time, since the photosensitive paper 105 is relatively transported with respect to the black/white LCD shutter array 103, the red line-shaped light, the green line-shaped light, and the blue line-shaped light are sequentially exposed onto the same place on the photosensitive paper 105. As a result, a two-dimensional print image can be obtained.
Generally speaking, in the conventional optical printing apparatus, light is exposed onto the photosensitive recording medium to form the gradation image in the above-described manner. To realize short printing time periods, super twisted nematic type liquid crystal, or ferroelectric liquid crystal is employed as the above-explained two different types of liquid crystal shutters (namely, color LCD shutter 101 and black/white LCD shutter 103). These liquid crystal shutters may respond to input image data in high speeds in the unit of millisecond by applying thereto an AC voltage having a frequency of approximately 10 KHz.
On the other hand, in the optical printing apparatus described in Japanese Patent Application Laid-open No. 62-134629, while the light measuring unit for measuring the light amount of the liquid crystal shutter is provided, even when the aging change occurs in the light source unit of the print head, the correction is carried out in such a manner that the variation in density can be reduced. Concretely speaking, first of all, the transmission light amounts of the respective color light in such a case that the liquid crystal shutter is brought into transparent conditions for a constant time period are measured by the photoelectric converting type light receiving unit. The measured light amount data is integrated, and the integrated data is A/D-converted. Subsequently, the image data is converted into the voltage application stop time of the LCD shutter by using the lookup table, and then, the voltage application stop time is corrected in response to the respective color light.
Also, another method is disclosed by which the variation contained in the density can be avoided in response to the information detected by the humidity and/or temperature detecting means.
The above-described conventional optical printing apparatuses own such a problem that the high image quality recording operation cannot be realized in low cost.
In other words, since these conventional optical printing apparatuses are arranged by employing the complex light receiving units, these printing apparatuses become high cost. Furthermore, the density variations caused by the difference in the exposure positions along the main scanning direction when the light source is positioned can hardly be corrected in high precision.
The present invention has been made to solve the above-explained problem, and therefore, has an object thereof to provide a low-cost optical printing apparatus capable of forming an image with uniform density.
Also, the present invention has another object thereof to provide a low-cost optical printing apparatus with a superior expanding characteristic, capable of highly precisely correcting input image data so as to avoid adverse influences caused by fluctuations of liquid crystal shutter elements and temperatures.
To achieved the above-described objects, an optical printing apparatus, according to a first aspect of the present invention, is featured by such an optical printing apparatus for selectively exposing light emitted from a print head onto a photosensitive recording medium to thereby form a gradation image, comprising: image data input means for inputting image data; image data correcting means for correcting the inputted image data in such a manner that a density fluctuation of the print head is deleted; reference level producing means for producing a reference level; comparing means for comparing multi-value data outputted from the image data correcting means with the reference level so as to convert the multi-value data into binary data; data transferring means for transferring the binary data outputted from the comparing means as head data to the print head; latch control means for latching data of the print data; and strobe control means capable of causing the print head to expose the light therefrom; whereby the print head is driven in response to the output results of the data transferring means, the latch control means, and the strobe control means to thereby form the gradation image.
Also, an optical printing apparatus, according to a second aspect of the present invention, is featured by that the latch control means outputs a latch signal, the intervals of which are substantially equal to constant within a recording time period of 1 line.
Also, an optical printing apparatus, according to a fourth aspect of the present invention, is featured by that the latch control means outputs a latch signal whose interval ratio is substantially equal to 1:2:4:8, - - - , within a recording time period of 1 line.
Also, an optical printing apparatus, according to a sixth aspect of the present invention, is featured by that the strobe control means outputs a strobe signal having a strobe width fitted to a recording characteristic.
Also, an optical printing apparatus, according to third, fifth, and seventh aspects of the present invention, is featured by that the intervals of the latch signal, or the strobe width of the strobe signal is controlled based upon temperature detection information.
Also, an optical printing apparatus, according to an eighth aspect of the present invention, is featured by that the optical printing apparatus is further comprised of; accumulated drive time storage means for storing drive time of the print head in an accumulation manner; and a density variation of the print head is corrected based on accumulated drive time.
Also, an optical printing apparatus, according to a ninth aspect of the present invention, is featured by that the image data correcting means corrects a density variation of the print head, which is caused by a difference in exposure positions along a main scanning direction.
Also, an optical printing apparatus, according to a tenth aspect of the present invention, is featured by that the image data correcting means outputs output data larger than a dynamic range of input data.
Also, an optical printing apparatus, according to an eleventh aspect of the present invention, is featured by such an optical printing apparatus for selectively exposing light emitted from a print head onto a photosensitive recording medium to thereby form a gradation image, comprising: image data input means for inputting image data; image data correcting means for correcting the inputted image data in such a manner that a density fluctuation of the print head is deleted; data transferring means for transferring the data outputted from the image correcting means as head data to the print head; and head data comparing means for comparing the head data in the print head; whereby the print head is driven in response to the output results of the data transferring means and the head data comparing means to thereby form the image.
Also, an optical printing apparatus, according to twelfth and thirteenth aspects of the present invention, is featured by that the fluctuation data of the image data correcting means is contained in the print head.